THE CHICAGO Teachers Union (CTU) announced late Monday night that it had reached a tentative agreement with the Chicago Public Schools (CPS) on a new contract, narrowly averting a strike.

The tentative deal was approved overwhelmingly by the union's big bargaining committee, made up of 40 rank-and-file teachers, shortly before a midnight deadline that would have triggered the second strike in four years on Tuesday.

There were several "no" votes from teachers who thought the union should take more time to go over the agreement before giving up its strike threat. But they said they agreed with those who voted "yes" that CPS had made major concessions on key issues in the contract fight.

Next, the 800 representatives of the union's House of Delegates will vote on the agreement, and if they approve, it will go to ratification by the union's 28,000 members.

The union and school officials have been locked in a bitter battle for well over a year since the teachers' old contract expired. Mayor Rahm Emanuel and his handpicked school board demanded sweeping concessions--like the ultimatum that teachers take over all contributions toward their pensions, which would have amounted to a 7 percent pay cut.

In the end, the city mostly caved on the so-called "pension pickup." Nothing will change for current CTU members or anyone still hired this year. Going forward, new hires will have to cover their pension contributions, as the city demanded of all teachers, but they will be compensated for the full amount with bigger paychecks.

Increases in base pay are meager, adding up to 4.5 percent in the final years of a four-year contract. But the union preserved the "steps and lanes" system that awards pay increases based on seniority and educational experience. That's a further defeat for Emanuel, who has demanded that the union abandon steps and lanes since taking office in 2011.

As in 2012, when the CTU's nine-day strike shook the city, the union appears to have pushed back CPS's harshest concession demands and won some long-sought contract provisions--thanks to a year of membership mobilization, two strike votes that showed teachers were committed to the fight, and a one-day strike on April 1 that Emanuel and school officials deemed illegal.

The union made some concessions. CPS will be able to increase CTU members' contributions to health care, but by less than 1 percent of total pay over the course of a year. That's a setback, but other unions have suffered worse in recent bargaining.

The new agreement also provides some new protection against layoffs--a significant issue in a school system where Emanuel recently closed 50 schools in one fell swoop in 2013.

There are first-time contract provisions on class size, specifically for kindergarten through 2nd grade. The tentative agreement also includes a formula for providing badly needed prep time for elementary school teachers.

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AS DURING the 2012 walkout that galvanized working-class Chicago, the CTU faced an arrogant City Hall, with Emanuel desperate to make teachers pay for the city's financial woes, along with every other public-sector worker.

This time, however, the union faced a war on another front: Illinois' Republican Gov. Bruce Rauner, the hedge-fund almost-billionaire, took office in 2015 with the aim of bringing public-sector unions to heel throughout the state. All year long, Rauner has been threatening to push CPS into bankruptcy so the state can take over and cancel its contracts with the CTU and other unions.

Chicago teachers didn't shrink from this two-sided offensive. The union held a strike authorization vote at the end of last year, and once again easily surpassed the undemocratic threshold of 75 percent support among all union members, not just those voting.

On April 1, the CTU went on a one-day strike--organized in coordination with other unions facing the brunt of Rauner's and Emanuel's budget cuts. The day of action not only brought together the coalition of parents, students and community members whose support was so important to the CTU in 2012, but it expanded the struggle to workers throughout the public sector.

With Emanuel's anti-union propaganda machine--led by the Chicago Tribune--running full tilt, teachers faced a more concerted backlash based on lies and distortions about pensions and other issues. But when it came time for another test of strength, CTU members once again voted overwhelmingly to strike.

Emanuel--whose popularity plunged last year following a scandal over the cover-up of the police killing of a 17-year-old Black youth, Laquan McDonald--knew the CTU was working to mobilize the alliance that took to the streets April 1. An open-ended strike could have finished off his already damaged political career. The mayor was facing the prospect of a mass picket line surrounding City Hall during his speech on the city budget, set for what would have been day one of the strike.

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THE TEACHERS' determination is the central reason that Emanuel and the school board backed down on many points.

Perhaps the most unexpected was the battle over the tax increment financing (TIF) system--a shady scheme run by the mayor that sets aside a portion of revenue from property taxes for development projects, many of them run by Emanuel's developer pals. With the threat of a strike looming, more and more people called on Emanuel to break open the TIF piggy bank to fund CPS.

As the October 11 strike deadline approached, one pressing demand of teachers--as well as students, teachers and community members--was for Emanuel to tap the $175 million TIF surplus to fund Chicago schools.

To the surprise of many, Emanuel made a concession on this front, agreeing that roughly half the TIF surplus would be directed to Chicago schools.

The mayor's political weakness and manifest willingness to make concessions led some on the bargaining team to argue that the CTU should press its advantage and strike to win even more. Others argued that the CTU--having already won gains on the union's key issues--should not move forward with a potentially lengthy strike.

That discussion will continue in the days to come, but we know that the credible threat of a strike--demonstrated clearly on April 1--forced Emanuel to retreat.

The CTU--despite repeated attacks in the form of school closures, layoffs and budget cuts--has maintained its capacity to fight. At the same time, the city's movement for education justice--a loosely knit group of parent, community, labor and faith-based activists in numerous organizations--was preparing active support for the CTU, as it had in 2012 and on Apri1 1 of this year.

In turn, the CTU's commitment to fighting for wider social issues is reflected in the proposed agreement. In addition to the smaller class sizes for the critical K-2 grades, the deal gives special education additional contract protections--and school counselors will be freed from paperwork in order to spend more time working with students.

This tentative agreement must still be approved by the CTU rank and file. But even if it is, the struggle will continue.

Rauner will continue to squeeze the state education budget, and Emanuel and CPS will try to chip away at the teachers' contract, while shortchanging students. The gains that the CTU made by mobilizing for a strike will only be protected by keeping up that fight.